Lockheed XV-4 Hummingbird

The Lockheed XV-4 Hummingbird (originally designated VZ-10) was a U.S. Army project to demonstrate the feasibility of using VTOL for a surveillance aircraft carrying target-acquisition and sensory equipment. It was designed and built by the Lockheed Corporation in the 1960s, one of many attempts to produce a V/STOL vertical take off/landing jet. Both prototype aircraft were destroyed in accidents.

Design and development

Vertical take-off lift was obtained by exhausting the engine flow downward through multiple nozzles. The nozzle thrust was augmented by a secondary flow of cold air. Unfortunately, performance was far below the estimates only 1.04 thrust-to-weight in practice and the prototype crashed on 10 June 1964, killing the pilot. The second aircraft was converted to lift jets instead, also crashing after several tests.

Rockwell's XFV-12 would be even less successful at producing lift by using engine exhaust to entrain cold air, in this case through flaps on the wings. The Lockheed F-35 Joint Strike Fighter would later employ a shaft-driven lift fan located in the fuselage.